Study on microstructure and magnetic domain structure in sputtered (Ni₆₆Fe₂₂Co₁₂) _x C_1−x nanocomposite films

Abstract

Composition and annealing temperature dependence of microstructure and magnetic domain structure in sputtered (Ni₆₆Fe₂₂Co₁₂) _x C_1−x nanocomposite films with x=10–75 at % were studied by X-ray diffraction and magnetic force microscopy (MFM). Films with x≤20 at % showed amorphous structures, and no domain structure could be found due to the disappearance of magnetocrystalline anisotropy. For the films with x=30–55 at %, face-centered cubic (fcc) NiFeCo nanocrystals encapsulated in graphite-like carbon could be found in the samples annealed beyond 400 °C, and stripe domains with typical dimension of 120–150 nm were observed. For the films with x≥62 at %, the as-deposited films went through a meta-stable stage at which a rhombohedral Ni₃C phase and fcc NiFeCo co-existed after annealing to a temperature between about 300–400 °C (dependent on composition). Upon further annealing to a sufficiently high temperature between about 350–500 °C, the carbide phase decomposed into fcc NiFeCo and graphite. While short-range domain structures were observed in the samples before the formation of carbide phase, long-range domain structure with dispersed domains in the meta-stable stage were observed. After the decomposition of carbide, large domains with typical size of 500–700 nm were observed due to the formation of large grain aggregators.